Mechanisms involved in hydrocarbon-induced malignant transformation will be studied in an in-vitro model system for chemical carcinogenesis which employs fibroblasts from mouse prostate. The metabolisms dependence of transformation induced by 7,12-dimethylbenz(a)anthracene will be investigated by comparing its transforming activity with that of different known metabolites, like non-K-region epoxides. Furthermore, the influence of inducers and inhibitors of microsomal mixed-function- oxidases activity and of radical scavengers on the transforming activity of this and related hydrocarbons will be studied. We will also continue to investigate the cell-cycle dependence of chemically induced malignant transformation and its possible causes, i.e., we will study the cell- cycle dependence of the hydrocarbon-DNA interaction and of hydrocarboninduced "repair DNA synthesis". Our finding that the synthetic double-stranded RNA, polyriboinosinic-polyribocytidylic acid, inhibits transformation by chemical carcinogens has led us into studying reverse transcriptase activity in non-treated cells, in cells shortly after treatment with chemical oncogens, and in cell lines which had been transformed by chemicals.